Donald, thanks for the further clarification.
Actually, the leangains site aroused my initial interest in IF, and my current approach is quite similar. In the above posts, I have used the terms "fasting" and "undereating" synonymously, which I see now is incorrect. Up to now I have done strict fasting, and not undereating.
I will stick to a fixed daily eating window then, and experiment with my pre-fasting food choices in order to minimize feelings of hunger during the fast.